Further studies of the energetics of interaction of antigen and specifically reactive immunocytes will be pursued. We will continue to use the model system we have developed of interaction between DNP conjugates and MOPC 315 murine myeloma cells which have on their surface hemogeneous immunoglobulin which is reactive with DNP. The major thrust of the new studies will be to investigate the effect of MOPC 315 protein on the capacity of these myeloma cells to interact with radio-labeled DNP conjugates. This will be an important test of the model which we have described (Bystryn et al. 1971 in Progress in Immunology Acad. Press, Inc., New York, p. 627) for the regulation of the immune response. In addition, we will continue to develop immunoabsorbants for use for the removal of antibody in vivo. We require immunoabsorbants with a larger capacity for binding antigen and which will be without toxic effects on the formed elements of the blood. We plan to use these immunoabsorbants in the development of an apparatus for removing in vivo antibody.